1. Field of the Invention
The invention relates to exercise devices and more particularly to a nonmotorized treadmill located in a tank of fluid which utilizes fluid resistance in exercising.
2. Description Of the Related Art
Aquatic exercise devices are well known, and a typical nonmotorized aquatic treadmill is shown in U.S. Pat. No. 4,576,376 issued to P. F. Miller on Mar. 14, 1986. The '376 patent discloses a solid endless belt looped around two rollers which are separated by a flat plate over which the belt slides in response to a walking action by a user. Nonmotorized treadmills are difficult to use because of the relatively high coefficient of friction between the bottom surface of the upper flight of the belt and the top surface of the flat plate in combination with the vertical force exerted by the weight of the user over the area of the user's feet. Further, the user creates varying horizontal forces during a striding motion which cause the user varying degrees of difficulty in pushing the treadmill belt smoothly over the plate. For example, at the beginning of a stride, when the user's front foot is planted and the rear foot leaves the surface, it is difficult for the user to create a horizontal force that is effective to push the belt over the plate toward the rear of the treadmill. Therefore, the nonmotorized treadmill is difficult to use at that point in the user's stride. As the stride progresses and the user's foot contacting the belt moves under and behind the user, a greater horizontal force component is exerted by the user on the belt; and the belt is more easily slidingly moved over the plate. Consequently, as the user moves from the initial portion of the stride toward the end of the stride, the degree of difficulty of moving the belt with respect to the plate changes from the most difficult to least difficult; and therefore, a smooth, consistent striding action and treadmill motion is not easily maintained.
The problem of reducing friction between the belt and the plate is addressed in the '376 patent by providing a perforated plate or providing a plate with a low friction upper surface or both. Friction may also be reduced by using a laminated belt as disclosed in U.S. Pat. No. 3,711,090 issued to V. G. Fiedler on Jan. 16, 1973. In the '090 patent, a belt is a laminated member which has an outer layer of conventional material which is comfortable to the user and has a adjoining laminated inner layer made of sheet material such as nylon, teflon, orlon, or other plastics having low friction coefficient characteristics. Further, low friction surfaces may also be used both on the top surface of the deck and the lower surface of the belt.
While the above treadmill constructions reduce the co-efficient of friction between the deck plate and the belt, there still is a substantial frictional force associated therewith.